1. Field of the Invention
The present invention relates to a semiconductor manufacturing technique and, more particularly, to a technique which is advantageously applied to high output MOSFETs (metal oxide semiconductor field effect transistors).
2. Description of the Prior Art
According to a study made by the inventor, exemplary semiconductor devices that generate high output and high heat include transistors referred to as “MOSFETs” which are used in electronic and electric apparatuses in all fields including power supplies and switches of battery-driven apparatuses, car electronics and controllers for driving motors.
An example of such MOSFETs that generate high output and high heat is disclosed in Japanese unexamined patent publication No. H8-64634. The MOSFET comprises a semiconductor pellet on which a field effect transistor (MOSFET element) is formed in a compact and plate-like configuration, a plurality of inner leads electrically connected to a surface electrode of the semiconductor pellet for electrically conducting the MOSFET element to the outside, a header for improving radiating performance and resin encapsulant formed by encapsulating the semiconductor pellet, the inner leads and a part of the header with resin. Each of the inner leads is mechanically and electrically connected through protruding terminals to a principal surface of the semiconductor pellet which is a circuit forming surface, and the header is bonded to a back surface of the semiconductor pellet which is the surface opposite to the principal surface.
In this MOSFET, since each of the inner leads is electrically connected to the surface electrode of the semiconductor pellet through the protruding terminals, external resistance is lower than that in the case of electrical connection using bonding wires. Further, since the header is separate from the inner leads, the header can be formed using a material having preferable radiating performance irrespective of the material of the inner leads, which makes it possible to improve the radiating performance of the header.
In the above-described MOSFET, the sum of electrical resistance of bonding wires, electrical resistance of aluminum wiring on the semiconductor pellet (hereinafter referred to as “external resistance”) and resistance inside the semiconductor pellet (hereinafter referred to as “internal resistance”) is the on resistance of the MOSFET as a whole. Substantially no problem is caused by the external resistance when the internal resistance is high.
However, when the magnitude of the external resistance exceeds about 50% of the entire resistance as a result of technical advances toward improvements to reduce the internal resistance, situations occur wherein the external resistance is not negligible.
In the above-described MOSFET, since each of the inner leads is electrically connected to the surface electrode of the semiconductor pellet through the protruding terminals, the external resistance can be lower than that in the case of electrical connection using bonding wires. However, since-an outer lead connected to each of the inner leads becomes long accordingly, there is a corresponding reduction of the effect of reducing the external resistance.
It is an object of the invention to provide a semiconductor device in which the external resistance can be significantly reduced and a method of manufacturing the same.
It is another object of the invention to provide a semiconductor device whose thermal resistance and packaging height can be reduced and a method of manufacturing the same.
The above and other objects and novel features of the invention will become apparent from the description of the present specification and the accompanying drawings.